Broadband distributed antenna system with non-duplexer isolator sub-system

ABSTRACT

Certain aspects and aspects of the present invention are directed to a distributed antenna system having a downlink communication path, an uplink communication path, and a non-duplexer isolator sub-system. The downlink communication path can communicatively couple a transmit antenna to a base station. The uplink communication path can communicatively couple a receive antenna to the base station. In one aspect, the non-duplexer isolator sub-system can be electronically configured for isolating uplink signals traversing the uplink communication path from downlink signals. In another aspect, a non-duplexer isolator sub-system can be configurable in one or more mechanical steps selecting a frequency response. In another aspect, a non-duplexer isolator sub-system can include an active mitigation sub-system.

RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 14/444,804,filed Jul. 28, 2014 and titled “Broadband Distributed Antenna SystemWith Non-Duplexer Isolator Sub-System,” which is a continuation of U.S.patent application Ser. No. 13/484,700, filed May 31, 2012 and titled“Broadband Distributed Antenna System With Non-Duplexer IsolatorSub-System,” now U.S. Pat. No. 8,818,299, which claims the benefit ofU.S. Provisional Application Ser. No. 61/492,077, filed Jun. 1, 2011 andtitled “Broadband Distributed Antenna System With Non-Duplexer IsolatorSub-System,” the contents of each of which are hereby incorporated byreference.

TECHNICAL FIELD

The present invention relates generally to telecommunications and, moreparticularly (although not necessarily exclusively), to isolating anuplink communication path from a downlink communication path in adistributed antenna system using a non-duplexer isolator sub-system.

BACKGROUND

A distributed antenna system (“DAS”) can be used to extend the coverageof a cellular communication system. For example, a DAS can extendcoverage to areas of traditionally low signal coverage within buildings,tunnels, or in areas obstructed by terrain features.

A DAS can include one or more master units in communication with carriersystems, such as base transceiver stations of cellular serviceproviders. The DAS can also include remote antenna units physicallyseparated from the master unit, but in communication with the masterunit via a serial link that may be copper, optical, or other suitablecommunication medium. The remote antenna units can wirelesslycommunicate with user devices positioned in a coverage area.

For example, the remote antenna units can be positioned in a building,tunnel, or other structure that prevents or limits communicationsdirectly with the carriers. Remote antenna units amplify downlinksignals received from the base station via a master unit and radiate thedownlink signal using an antenna. An antenna unit recovers uplinksignals from mobile user equipment and provides the uplink signals tothe master unit. The uplink signals are summed together and providedback to the base station.

A remote antenna unit typically includes at least one duplexer forseparating uplink signals and downlink signals. Duplexers isolate atransmitter output from a receiver input by allowing frequencies withinthe downlink band to be provided from the transmitter output to theantenna and allowing frequencies within the uplink band to be providedfrom the antenna output to the receiver. Isolating a transmitter outputfrom a receiver input prevents downlink signals from interfering withuplink signals. Isolating a transmitter output from a receiver inputalso prevents the receiver from recovering transmitter-generated noisethat would desensitize the receiver.

Duplexers, however, are undesirable for a variety of reasons. Duplexersuse fixed filters tuned to the specific frequencies. A DAS covers a widerange of frequencies for flexibility and cost reduction reasons. Theallocation of these frequencies into bands may change over time and aretypically different in different countries. Re-tuning a duplexerinvolves a multi-step tuning procedure to change the position of amultitude of tuning screws. Re-tuning a ceramic duplexer may involve theuse of a hand tool to re-shape the duplexer. The manual configurationsuse a network analyzer to identify the resulting change in the operationof the duplexer. Duplexers using fixed filters provide little or noflexibility to respond to changes in frequency band allocation.

One solution for isolating uplink signals from downlink signals withouta duplexer is an RF-impermeable layer separating transmit and receiveantennas. This solution is generally sufficient to preventtransmitter-generated noise from desensitizing the receiver, butadditional isolation implemented with or without the RF impermeablelayer may be desired. Therefore, systems and methods are desirable thatprovide additional signal isolation without the use of a duplexer.

SUMMARY

One aspect of the present invention is directed to a distributed antennasystem having a downlink communication path, an uplink communicationpath, and a non-duplexer isolator sub-system. The downlink communicationpath can communicatively couple a transmit antenna to a base station.The uplink communication path can communicatively couple a receiveantenna to the base station. The non-duplexer isolator sub-system can beelectronically configured for isolating uplink signals traversing theuplink communication path from downlink signals.

Another aspect is directed to a distributed antenna system having adownlink communication path, an uplink communication path, and anon-duplexer isolator sub-system. The downlink communication path cancommunicatively couple a transmit antenna to a base station. The uplinkcommunication path can communicatively couple a receive antenna to thebase station. The non-duplexer isolator sub-system can include a filterdevice configurable in one or more mechanical steps selecting afrequency response.

Another aspect is directed to a distributed antenna system having adownlink communication path, an uplink communication path, and anon-duplexer isolator sub-system. The downlink communication path cancommunicatively couple a transmit antenna to a base station. The uplinkcommunication path can communicatively couple a receive antenna to thebase station. The non-duplexer isolator sub-system can include an activemitigation sub-system

These illustrative aspects and features are mentioned not to limit ordefine the invention, but to provide examples to aid understanding ofthe inventive concepts disclosed in this application. Other aspects,advantages, and features of the present invention will become apparentafter review of the entire application.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a distributed antenna system in which anon-duplexer isolator sub-system can be disposed according to oneaspect.

FIG. 2 is a block diagram of a non-duplexer isolator sub-system disposedin the distributed antenna system of FIG. 1 according to one aspect.

FIG. 3 is a schematic view of a non-duplexer isolator sub-system thatincludes filter devices configured via one or more mechanical stepsaccording to one aspect.

FIG. 4 is a partial schematic view of a non-duplexer isolator sub-systemthat includes electronically configurable filters according to oneaspect.

FIG. 5 is a partial schematic view of a non-duplexer isolator sub-systemthat includes active analog mitigation according to one aspect.

FIG. 6 is a partial schematic view of a non-duplexer isolator sub-systemthat includes digital analog mitigation according to one aspect.

FIG. 7 is a partial schematic view of a non-duplexer isolator sub-systemthat includes active digital mitigation according to one aspect.

FIG. 8 is a schematic view of the non-duplexer isolator sub-systemincluding an adaptive filter for active digital mitigation according toone aspect.

FIG. 9 is a schematic view of the non-duplexer isolator sub-system usingactive mitigation including circuitry for mitigating uplink frequencycomponents overlapping caused by overlapping uplink and downlinkfrequency bands according to one aspect.

FIG. 10 is a schematic view of the non-duplexer isolator sub-systemusing active mitigation including circuitry for removing nonlineardistortion from an uplink signal following active digital mitigationaccording to one aspect.

FIG. 11 is a schematic view of the non-duplexer isolator sub-systemusing active mitigation including circuitry for separately removingnonlinear distortion from the active mitigation signal and the uplinksignal prior to active digital mitigation according to one aspect.

FIG. 12 is a flow chart illustrating a process for configuring an uplinkgain adjust device according to one aspect.

DETAILED DESCRIPTION

Certain aspects and features of the present invention are directed to anon-duplexer isolator sub-system for a DAS. A non-duplexer isolatorsub-system according to some aspects can isolate uplink signalstraversing an uplink communication path in the system from downlinksignals and derivatives thereof, obviating the need for a duplexer inthe DAS.

In some aspects, the non-duplexer isolator sub-system may include one ormore configurable filters. The configurable filters may be positioned inone or both of a downlink communication path or an uplink communicationpath. The configurable filters can reject or attenuate spurious signalsthat may leak into, or otherwise be present in, the uplink communicationpath. In some aspects, the configurable filters are configured via oneor more mechanical steps selecting a frequency response for therespective filters. In other aspects, the configurable filters areconfigured electronically by a control signal.

In one aspect, the non-duplexer isolator sub-system includes circuitrycapable of performing active mitigation of undesirable signals.Mitigating an undesirable signal can include cancelling the undesirablesignal or otherwise minimizing the undesirable signal. The circuitry caninclude a filter that can adjust the gain and shift the phase of adownlink reference signal to generate a mitigation signal. Themitigation signal can be summed with the uplink signal to mitigateundesirable signal components included in the uplink signal. Analog ordigital filters can be used to generate the mitigation signal. In someaspects, the analog or digital filters are adaptive filters that canadjust a frequency response dynamically. In other aspects, the analog ordigital filters are non-adaptive filters that are configured to have astatic frequency response that may be configured manually.

Detailed descriptions of these aspects are discussed below. Theseillustrative examples are given to introduce the reader to the generalsubject matter discussed here and are not intended to limit the scope ofthe disclosed concepts. The following sections describe variousadditional aspects and examples with reference to the drawings in whichlike numerals indicate like elements, and directional descriptions areused to describe the illustrative aspects but, like the illustrativeaspects, should not be used to limit the present invention.

FIG. 1 schematically depicts a DAS 10 in which a non-duplexer isolatorsub-system can be disposed according to one aspect. The DAS 10 can becommunicatively coupled to at least one base station 12 via a wired orwireless communication medium. The DAS 10 can be positioned in an areasuch as a building environment to extend wireless communicationcoverage. The DAS 10 can include one or more remote antenna units 14that are distributed in the environment to provide coverage within aservice area of the DAS 10. The remote antenna units 14 can service anumber of different user devices 16, such as cellular phones, operatingin the environment of the DAS 10. Each remote antenna unit 14 caninclude at least one antenna 18. Antenna 18 may include one or moreantenna elements.

Remote antenna units 14 can be communicatively coupled to one or moremaster units 22 via any communication medium capable of carrying signalsbetween the master unit 22 and remote antenna unit 14. Examples of asuitable communication medium can include (but are not limited to)copper, optical, and microwave link. Master units 22 can process thesignals from remote antenna units 14 to interface appropriately with thebase station 12. A system controller 24 can control the operation ofeach of the master units 22 for processing the signals 26 associatedwith the remote antenna units 14. The signals 26 of the remote antennaunits 14 may be the uplink and downlink signals of the DAS 10 forcommunicating with user devices 16.

Although the DAS 10 is depicted as including two master units 22 andfour remote antenna units 14, any number (including one) of each ofmaster units 22 and remote antenna units 14 can be used. Furthermore, aDAS 10, according to some aspects, can be implemented without systemcontroller 24.

FIG. 2 depicts a non-duplexer isolator sub-system 105 disposed in theDAS 10 that eliminates the need for a duplexer. The DAS 10 in FIG. 2also includes a downlink communication path 104 and an uplinkcommunication path 108. The non-duplexer isolator sub-system 105 canisolate signals traversing the uplink communication path 108 fromsignals or other signal components of the downlink communication path104.

The downlink communication path 104 and the uplink communication path108 can be communicatively coupled to the antenna 18. In some aspects,the antenna 18 includes two antennas: a transmit antenna 106 and areceive antenna 107. In other aspects, the antenna 18 includes oneantenna that can both transmit and receive RF signals. The transmitantenna 106 can radiate RF signals having information from the basestation 12 to the user devices 16. The receive antenna 107 can recoversignals from user devices 16 to be provided to base station 12.

In some aspects, non-duplexer isolator sub-system 105 is disposed in aremote antenna unit 14. In other aspects, non-duplexer isolatorsub-system 105 is disposed in a master unit 22. The non-duplexerisolator sub-system 105 may alternatively be disposed partially within amaster unit 22 and partially within a remote antenna unit 14.

The non-duplexer isolator sub-system 105 according to various aspectsmay be any non-duplexer device or collection of components. Thenon-duplexer isolator sub-system 105 may also incorporate componentsthat prevent the formation of a feedback loop. These components,described in further detail below, can attenuate the gain of both uplinkand downlink signal to prevent system instability in the DAS 10. Certainfeatures of a suitable non-duplexer isolator sub-system are describedbelow.

Mechanically Configurable Filter

FIG. 3 schematically depicts a non-duplexer isolator sub-system thatincludes a filter device configured via one or more mechanical stepsaccording to one aspect. The non-duplexer isolator sub-system in FIG. 3includes both a mechanically configurable filter 230 in the downlinkcommunication path 104 and a mechanically configurable filter 238 in theuplink communication path 108. In other aspects, the mechanicallyconfigurable filter includes a mechanically configurable filter in onlyone of the downlink communication path 104 or the uplink communicationpath 108.

The DAS 10 includes the downlink communication path 104 and the uplinkcommunication path 108 communicatively coupled to the base station 12.Downlink signals are provided from base station 12 to the downlinkcommunication path 104. Transmit antenna 106 can radiate downlinksignals traversing the downlink communication path 104 to the userdevices 16. Receive antenna 107 can recover uplink signals from userdevices 16 and can provide the uplink signals to the uplinkcommunication path 108. Signals traversing uplink communication path 108are provided to base station 12.

In some aspects, the DAS 10 may include a splitter-combiner that canconnect downlink communication path 104 and uplink communication path108 to a common port communicatively coupled to base station 12. Thesplitter-combiner can receive signals from base station 12 and splitdownlink signals to be transmitted from the uplink signals to beprovided to the base station 12. The splitter-combiner can providedownlink signals to downlink communication path 104. Thesplitter-combiner can provide uplink signals to base station 12.

FIG. 3 also depicts components that may be included in the downlinkcommunication path 104 and components that may be included in the uplinkcommunication path 108. The downlink communication path 104 can includea local oscillator 203, a mixer 206, an anti-aliasing filter 209, ananalog-to-digital converter 212, a digital IF filter 215, adigital-to-analog converter 218, an analog filter 221, a mixer 224, alocal oscillator 226, a power amplifier 227, and a mechanicallyconfigurable filter 230.

The mixer 206 and the local oscillator 203 can down-convert the downlinksignal received from the base station 12 from RF to an intermediatefrequency (“IF”).

The anti-aliasing filter 209 can reduce aliasing from converting thedownlink signal from analog to digital. For example, the anti-aliasingfilter 209 can reject signal components at frequencies greater thanone-half the sampling frequency of analog-to-digital converter 212. Theanti-aliasing filter 209 can also reject signal components in one ormore adjacent Nyquist zones. In some aspects, the anti-aliasing filter209 can be a surface acoustic wave (“SAW”) filter. The analog-to-digitalconverter 212 can convert the analog downlink signal to a digitaldownlink signal for communication via a serial link between a masterunit, which includes the analog-to-digital converter 212, and a remoteunit. The digital IF filter 215 can receive the digital downlink signaland reduce the gain of the downlink digital signal.

The digital-to-analog converter 218 can convert the downlink signal toan analog signal. The analog filter 221 can receive the analog downlinksignal and remove any aliases resulting from converting the digitalsignals to analog. The mixer 224 and the local oscillator 226 canup-convert the downlink signal to the appropriate RF frequency. Thepower amplifier 227 can amplify the downlink signal to the output powerfor transmission.

Prior to the transmit antenna 106 broadcasting the downlink signal,mechanically configurable filter 230 can filter the downlink signal toisolate receive antenna 107 from undesirable signal components.Undesirable signal components may be generated by components of thedownlink communication path 104 while processing the downlink signal, orotherwise. Undesirable signal components may include signals, other thanthe desired downlink signal, transmitted by transmit antenna 106 at afrequency within the frequency band of receive antenna 107. Undesirablesignal components may also include harmonics of the transmit RFfrequency of downlink signals.

Undesirable signal components may also include signals generated by themixer 224 and the local oscillator 226 during up-conversion to RF. Forexample, during up-conversion, the mixer 224 can process the IF downlinksignal and a signal received from the local oscillator 226. The outputsignal of the mixer 224 can include two signals. One signal may be theRF downlink signal at a frequency equal to the sum of the frequencies ofthe IF downlink signal and the signal received from local oscillator226. The other signal may be an image signal at a frequency equal to thedifference of the frequencies of the IF downlink signal and the signalreceived from local oscillator 226. The image signal, as well as anyharmonics of the output signals of mixer 224, may be undesirable signalcomponents.

The mechanically configurable filter 230 may be any suitable filterdevice that can be configured in one or more mechanical steps selectinga frequency response. A mechanical step can be a physical step, such as(but not limited to) moving a switch between positions. In some aspects,a mechanical step can be executed by one or more devices in response toa control signal provided to the mechanically configurable filter. Inother aspects, a mechanical step can be executed by an operator.

The mechanically configurable filter 230 may include a bandpass filterthat passes the desired frequency band of the downlink signals. Thebandpass filter can reject or attenuate undesirable signal components.By rejecting or attenuating undesirable signal components that may betransmitted at frequencies to which receive antenna 107 may be tuned,the mechanically configurable filter 230 can isolate uplinkcommunication path 108 from downlink communication path 104.

The desired downlink frequency band of mechanically configurable filter230 can be manually selected in a single physical step. A singlephysical step may include using an RF switch to select a channelcorresponding to a particular frequency band on a multi-channel switchfilter bank.

In some aspects, some components of downlink communication path 104 maybe disposed in master unit and other components may be disposed within aremote antenna unit. The components disposed in a master unit caninclude a local oscillator 203, a mixer 206, an anti-aliasing filter209, and an analog-to-digital converter 212. The components disposedwithin a remote antenna unit can include a digital IF filter 215, adigital-to-analog converter 218, an analog filter 221, a mixer 224, alocal oscillator 226, a power amplifier 227, and a mechanicallyconfigurable filter 230. In these aspects, the output of theanalog-to-digital converter 212 is coupled to the input of the digitalIF filter 215 via a serial communications link.

In other aspects, all components of downlink communication path 104 maybe disposed in a master unit or in a remote antenna unit. Although FIG.3 depicts the downlink communication path 104 receiving signals directlyfrom the base station 12, a downlink communication path 104 may receivesignals from a base station 12 via one or more intermediate componentsor devices. For example, if all components of a downlink communicationpath 104 are disposed in a remote antenna unit, the downlinkcommunication path 104 can receive signals from a base station 12 via amaster unit.

The uplink communication path 108 can include a low noise amplifier 236,a mechanically configurable filter 238, a local oscillator 239, a mixer242, an amplifier 245, an anti-aliasing filter 248, an amplifier 251, ananalog-to-digital converter 254, a digital IF filter 257, adigital-to-analog converter 263, an analog filter 266, a localoscillator 269, a mixer 272, a power amplifier 275, and an uplink gainadjust device 278.

The receive antenna 107 can recover uplink signals from a mobile userdevice and provide uplink signals to the low noise amplifier 236. Thelow noise amplifier 236 can amplify uplink signals recovered by thereceive antenna 107.

A mechanically configurable filter 238 can filter the uplink signal toreject undesirable signal components. Undesirable signal components mayinclude signals, other than the desired uplink signal, such as thosedescribed previously, which can include harmonics of the transmitteddownlink signal and image signals and harmonics from the mixer 224 andthe local oscillator 226.

A mechanically configurable filter 238 may include a bandpass filterthat can pass a desired uplink frequency band. The bandpass filter canreject or attenuate undesirable signal components at frequencies outsidethe desired uplink frequency band. By filtering the uplink signals,mechanically configurable filter 238 can isolate the uplinkcommunication path 108 from downlink communication path 104.

The uplink signal can be further processed by local oscillator 239 andmixer 242 to down-convert the uplink signal from RF to IF. The amplifier245 can amplify the down-converted uplink signal. The anti-aliasingfilter 248 can reject signal components at frequencies greater thanone-half the sampling frequency of analog-to-digital converter 254, aswell as frequencies within one or more adjacent Nyquist zones, to reducealiasing from converting the uplink signal from analog to digital. Insome aspects, the anti-aliasing filter 248 may be a SAW filter. Theamplifier 251 can amplify the uplink signal. Analog-to-digital converter254 can convert the analog uplink signal to a digital uplink signal thatmay be transmitted over a serial link from a remote unit to a masterunit. The digital IF filter 257 can further limit the gain of the uplinksignal.

The digital-to-analog converter 263 can convert the uplink digitalsignal to an analog signal. The analog filter 266 can filter the signalto prevent aliasing that may result from converting the digital signalsto analog. The local oscillator 269 and the mixer 272 can up-convert theuplink signal to RF for transmission to the base station 12. The poweramplifier 275 can amplify the uplink signal prior to transmission to thebase station 12.

The uplink gain adjust device 278 can compensate for transmitter noiseon the uplink signal. For example, the uplink gain adjust device 278 canincrease the uplink signal gain to prevent that the signal-to-noiseratio of the uplink signal from decreasing below an acceptablethreshold. The uplink signal from gain adjust device 278 can be providedto the base station 12.

In some aspects, some components of the uplink communication path 108are disposed in a master unit and other components of uplinkcommunication path 108 are disposed in a remote antenna unit. Thecomponents disposed in a remote antenna unit may include the low noiseamplifier 236, the mechanically configurable filter 238, the localoscillator 239, the mixer 242, the amplifier 245, the anti-aliasingfilter 248, the amplifier 251, and the analog-to-digital converter 254.The components disposed in a master unit may include the digital IFfilter 257, the digital-to-analog converter 263, the analog filter 266,the local oscillator 269, the mixer 272, the power amplifier 275, andthe uplink gain adjust device 278. The analog-to-digital converter 254can be serially coupled to the digital IF filter 257.

Although FIG. 3 depicts the uplink communication path 108 providingsignals directly to the base station 12, an uplink communication path108 may provide signals to a base station 12 via one or moreintermediate components or devices. For example, if all components of anuplink communication path 108 are disposed in a remote antenna unit, theuplink communication path 108 can provide signals to a base station 12via a master unit.

In some aspects, the uplink communication path 108 may include a digitalsummer in a master unit. The digital summer can be communicativelycoupled to the output of digital IF filter 257. The digital summer cansum uplink signals from various remote antenna units before providingthe uplink signals to the base station 12.

Electronically Configurable Filter

FIG. 4 schematically depicts a non-duplexer isolator sub-systemaccording to one aspect that includes electronically configurablefilters 310, 312 disposed in the downlink communication path 104 and theuplink communication path 108, respectively. As with the mechanicallyconfigurable filters depicted in FIG. 3, a DAS 10 according to someaspects can include only one of the electronically configurable filters310, 312 instead of both electronically configurable filters 310, 312.

FIG. 4 depicts a non-duplexer sub-system using signal processing blocks.The signal processing blocks of FIG. 4 may be implemented usingcomponents such as those as depicted in FIG. 3. Other configurations andaspects may of course be utilized.

The downlink communication path 104 can include a digital-to-analogconversion block 306 and an up-conversion block 308. The uplinkcommunication path 108 can include a down-conversion block 314 and ananalog-to-digital conversion block 316.

The electronically configurable filters 310, 312 can isolate signalstraversing the uplink communication path 108 from the downlinkcommunication path 104. The electronically configurable filters 310, 312may be bandpass filters that can be configured electronically. Thebandpass filters can remove undesirable signal components, such astransmitter-generated noise and spurious outputs of up-conversion block308, from uplink signals by passing the desired downlink or uplinkfrequency band and rejecting undesirable signal components outside thedesired frequency band.

The electronically configurable filters 310, 312 can be configured bymodifying the frequency response in response to receiving an electroniccontrol signal. The frequency response may include the desired frequencyband to be passed. The electronic control signal may be provided by anexternal controller. An example of an external controller is a computingdevice, such as (but not limited to) a laptop or a server, that iscommunicatively coupled to the electronically configurable filter beingconfigured. The electronically configurable filter can include amicroprocessor or similar device that can respond to the electroniccontrol signal by configuring the electronically configurable filter tohave a desired frequency response.

In some aspects, electronically configuring the electronicallyconfigurable filters 310, 312 can include modifying the frequencyresponse by electrically tuning the electronically configurable filters310, 312 in response to the electronic control signal. In other aspects,electronically configuring the electronically configurable filters 310,312 can include modifying the frequency response via one or moremechanical steps executed in response to the electronic control signal.

The electronically configurable filters 310, 312 may include anybandpass filter for which the frequency response can be adjusted inresponse to an electronic control signal. In some aspects, the bandpassfilter includes one or more varactor diodes. The frequency response ofthe bandpass filter can be adjusted by varying the capacitance of one ormore varactor diodes in response to the electronic control signal. Thecapacitance of the varactor diodes can be varied by applying varyinginput voltages to respective terminals of the varactor diodes. Alteringthe capacitance of one or more varactor diode can alter both the centerfrequency and bandwidth of the bandpass filter. In some aspects, thesource of the applied voltage may be disposed in the electronicallyconfigurable filter, with applied voltage levels controlled by themicroprocessor in response to receiving an electronic control signalfrom the external controller. In other aspects, the source of theapplied voltage may be an external device controlled by the externalcontroller.

Active Analog Mitigation

FIG. 5 schematically depicts a non-duplexer isolator sub-system thatincludes active analog mitigation circuitry disposed in uplinkcommunication path 108. The active analog mitigation circuitry mayinclude an analog summer 404 that receives a downlink mitigation signalfrom a configurable analog filter 403 in a reference communication path402. The reference communication path 402 may include a path from acoupled point at the output of power amplifier 227 to an input of theanalog summer 404. A downlink reference signal from the output of poweramplifier 227 can traverse the reference communication path 402.

A configurable analog filter 403 can be positioned in the referencecommunication path 402 and communicatively coupled to the poweramplifier 227 to receive the downlink reference signal. The configurableanalog filter 403 can generate a downlink mitigation signal from thedownlink reference signal by adjusting the gain and shifting the phaseof the downlink reference signal. The downlink mitigation signal may beequal in amplitude to and 180 degrees out of phase with undesirablesignal components generated in downlink communication path 104 andrecovered by receive antenna 107.

An analog summer 404 can be positioned in the uplink communication path108. The output of configurable analog filter 403 can be communicativelycoupled to one of the inputs of analog summer 404. Another input of theanalog summer 404 can be communicatively coupled to the receive antenna107. The analog summer 404 can receive the downlink mitigation signalfrom the configurable analog filter 403 and sum the downlink mitigationsignal with the uplink signal to mitigate any undesirable signalcomponents present in the uplink signal. Mitigating undesirable signalcomponents can include, for example, cancelling the undesirable signalcomponents present in the uplink signal. The analog summer 404 canprovide the uplink signal to the low noise amplifier 236. The uplinksignal can traverse the remainder of uplink communication path 108 asdepicted in FIG. 3.

The frequency response of the configurable analog filter 403 may beconfigured via a test signal at the configuration of the DAS 10. Forexample, a test signal can be transmitted by the transmit antenna 106and any signal detected on the uplink communication path 108 can beidentified as the undesirable signal component generated by thetransmission of the test downlink signal. The frequency response of theconfigurable analog filter 403 may then be adjusted via electronic ormanual processes to generate a downlink mitigation signal equal inamplitude to and 180 degrees out of phase with the undesirable signalcomponent. In some aspects, the configurable analog filter 403 mayinclude an analog vector modulator capable of adjusting the phase andgain of the downlink mitigation signal.

In some aspects, the configurable analog filter 403 may include anadaptive filter. The adaptive filter can be dynamically optimized by amicroprocessor utilizing an iterative adaptation algorithm. The inputsto the iterative adaptation algorithm can be a downlink referencesignal, such as the output signal from the power amplifier 227, and anerror signal, such as the output signal from the analog summer 404. Themicroprocessor can apply the iterative adaptation algorithm to optimizethe frequency response of the configurable analog filter 403. Theconfigurable analog filter 403, applying an optimized frequencyresponse, can generate a downlink mitigation signal correlated with theundesirable signal component from the downlink communication path 104.In some aspects, the iterative adaptation algorithm may be a least meansquare algorithm.

Although aspects depicted in FIGS. 3-5 have been described with respectto a DAS 10 using digital signals, the systems and processes describedabove can be implemented using other systems, such as an analog DAS or arepeater system including one or more antennas for transmitting andreceiving analog RF signals.

Active Digital Mitigation

FIG. 6 schematically depicts a non-duplexer isolator sub-system havingactive digital mitigation circuitry disposed in uplink communicationpath 108 and using a sample downlink signal. The active digitalmitigation circuitry may include a digital summer 405 that receives adownlink mitigation signal traversing a reference communication path406. The reference communication path 406 may include a path from acoupled point at the input of the digital-to-analog conversion block 306to an input of the digital summer 405. The reference communication path406 may include a configurable digital filter 408, a digital-to-analogconversion block 410, an up-conversion block 412, and an amplifier 414.

A downlink reference signal can traverse the reference communicationpath 406. The configurable digital filter 408 can generate a downlinkmitigation signal from the downlink reference signal by adjusting thegain and shifting the phase of the downlink reference signal. Thedownlink mitigation signal may be equal in amplitude to and 180 degreesout of phase with undesirable signal components generated in downlinkcommunication path 104 and recovered by receive antenna 107. An exampleof a configurable digital filter 408 can be a digital least-mean-squareadaptive filter.

The digital-to-analog conversion block 410, the up-conversion block 412,and the amplifier 414, can process the downlink reference signal in thesame manner as the corresponding components included in a parallelsection of the downlink communication path 104 that can process thedownlink signal.

The output of the amplifier 414 can be communicatively coupled to one ofthe inputs of the digital summer 405. Another input of the digitalsummer 405 can be communicatively coupled to the receive antenna 107.The digital summer 405 can receive the downlink mitigation signal andsum the downlink mitigation signal with the uplink signal to mitigateany undesirable signal components present in the uplink signal. Thedigital summer 405 can provide the uplink signal to the low noiseamplifier 236. The uplink signal can traverse the remainder of uplinkcommunication path 108 as depicted in FIG. 3.

An adaptation algorithm 418 can receive an uplink reference signalsampled from the uplink communication path 108. A microprocessor canexecute the adaptation algorithm 418 to iteratively adjust a frequencyresponse of the configurable digital filter 408 based on the uplinkreference signal.

FIG. 7 depicts a non-duplexer isolator sub-system that includes activedigital mitigation circuitry. FIG. 7 also depicts the downlinkcommunication path 104, the uplink communication path 108, and areference communication path 503. The active digital mitigationcircuitry may include a digital summer 530 that receives a downlinkmitigation signal from a configurable digital filter 521 in a referencecommunication path 503.

FIG. 7 schematically depicts the components that may be included in theuplink communication path 108 and the corresponding components that maybe included in the reference communication path 503 in addition to theconfigurable digital filter 521. The reference communication path 503can include a mixer 506 coupled to a local oscillator 239, an amplifier509, an analog IF filter 512, an amplifier 515, and an analog-to-digitalconverter 518. FIG. 7 also depicts the downlink communication path 104using signal processing blocks.

The reference communication path 503 may be a path from the output ofthe power amplifier 227 to one of the inputs of the digital summer 530.The power amplifier 227 can provide a downlink reference signal to theconfigurable digital filter 521 via the reference communication path503. A mixer 506 (communicatively coupled to local oscillator 239), anamplifier 509, an analog IF filter 512, an amplifier 515, and ananalog-to-digital converter 518 can process the downlink referencesignal in the same manner as the corresponding components included in aparallel section of uplink communication path 108 that can process theuplink signal.

The configurable digital filter 521 can be positioned in the referencecommunication path 503. The configurable digital filter 521 can receivea downlink reference signal from analog-to-digital converter 518 andgenerate a downlink mitigation signal. To generate the downlinkmitigation signal, the configurable digital filter 521 can adjust thegain and phase of the downlink reference signal. The downlink mitigationsignal may be equal in amplitude to and phase shifted 180 degrees fromany undesirable signal component generated in downlink communicationpath 104 and recovered by receive antenna 107.

The digital summer 530 can be positioned in the uplink communicationpath 108. The output of the configurable digital filter 521 can becommunicatively coupled to one of the inputs of the digital summer 530.Another input of the digital summer 530 may be communicatively coupledto the output of the analog-to-digital converter 254.

The digital summer 530 can receive a downlink mitigation signal fromconfigurable digital filter 521 and a digital uplink signal from theanalog-to-digital converter 254. The digital summer 530 can sum thedownlink mitigation signal with the uplink signal to mitigate anyundesirable signal components present in the uplink signal. The digitalsummer 530 can provide the uplink signal to the digital-to-analogconverter 263. The uplink signal can traverse the remainder of uplinkcommunication path 108.

In some aspects, a non-duplexer isolator sub-system may include one ormore devices for optimizing the frequency response of a configurabledigital filter, as depicted in FIGS. 7 through 10. Optimizing thefrequency response can allow the configurable digital filter todynamically generate an accurate downlink mitigation signalcorresponding to an undesirable signal component.

The aspect depicted in FIG. 8 includes the downlink communication path104, the uplink communication path 108, a reference communication path626, the transmit antenna 106, and the receive antenna 107.

The downlink communication path 104 may include a digital-to-analogconverter 600, an analog filter 602, a mixer 604, a local oscillator606, an image reject filter 608, and a power amplifier 610. Thedigital-to-analog converter 600 can convert digital downlink signals toanalog signals. The analog filter 602 can remove any aliases resultingfrom converting the digital downlink signals to analog signals. Themixer 604 and the local oscillator 606 can up-convert downlink signalsto RF. The image reject filter 608 can reject or attenuate any outputsignal from mixer 604 at an image frequency of the desired downlinkfrequency. The power amplifier 610 can amplify the downlink signal to anoutput power for transmission.

The uplink communication path 108 may include an analog filter 614, alow noise amplifier 616, a mixer 618, a local oscillator 620, ananti-aliasing filter 622, an analog-to-digital converter 624, and adigital summer 642. The analog filter 614 can reject or attenuate noiseon uplink signals recovered by receive antenna 107. The low noiseamplifier 616 can amplify the uplink signal. The mixer 618 and the localoscillator 620 can down-convert the uplink signal to IF. Theanti-aliasing filter 622 can reject signal components at frequenciesgreater than one-half the sampling frequency of the analog-to-digitalconverter 624, as well as frequencies within one or more adjacentNyquist zones. Rejecting signal components at frequencies greater thanone-half the sampling frequency of the analog-to-digital converter 624and at frequencies within one or more adjacent Nyquist zones can reducealiasing from converting the uplink signal from analog to digital. Theanalog-to-digital converter 624 can convert the analog uplink signal toa digital uplink signal. The digital summer 642 can sum the downlinkmitigation signal from the configurable digital filter 640 with theuplink signal from the analog-to-digital converter 624.

The reference communication path 626 may include an attenuator 612, ananalog filter 628, a low noise amplifier 630, a mixer 634, ananti-aliasing filter 636, an analog-to-digital converter 638, and aconfigurable digital filter 640.

As depicted in FIG. 8, the downlink mitigation signal can be generatedfrom a downlink reference signal traversing the reference communicationpath 626. The attenuator 612 can attenuate the downlink reference signalsuch that the downlink reference signal power at the input to the analogfilter 628 is equal to the power of any undesirable signals recovered bythe receive antenna 107 at the input to the analog filter 614.Equalizing the power of the downlink reference signal and theundesirable signals recovered by the receive antenna 107 can ensure thatthe mitigation signal generated by the configurable digital filter 640can mitigate non-linear distortion signals on uplink communication path108.

Non-linear distortion on uplink communication path 108 can be caused bythe mixer 618 receiving undesirable signals recovered by the receiveantenna 107. Undesirable signals received by the mixer 618 can beprocessed by the mixer 618. The output of the mixer 618 can includenon-linear distortion signal components at intermodulation frequencies.The non-linear distortion signal components at intermodulationfrequencies can result from the mixing of undesirable signals andharmonic responses from the local oscillator 620 and the input RFsignals to the mixer 618. The output of the mixer 634 can also includenon-linear distortion signal components.

The attenuator 612 can attenuate the power of the downlink referencesignal such that the ratio between the undesirable signal power and thenon-linear distortion signal power for signals traversing the uplinkcommunication path 108 is equal to the ratio between the downlinkreference signal power and the non-linear distortion signal power forsignals traversing the reference communication path 626. Equalizingthese ratios can allow the mitigation signal generated from thereference signal to mitigate both the undesirable signals and thenon-linear distortion signal components on the uplink communication path108. The attenuation provided by the attenuator 612 can be dynamicallyadjusted by a microprocessor executing the adaptation algorithm 644. Theoperation of the microprocessor executing the adaptation algorithm 644is described in further detail below.

The analog filter 628 and the low noise amplifier 630 can perform thesame functions as the corresponding components included in the uplinkcommunication path 108. The mixer 634, communicatively coupled to localoscillator 620, can down-convert the downlink reference signal. Theanti-aliasing filter 636 can reduce aliasing from converting thedownlink reference signal from analog to digital by rejecting signalcomponents at frequencies greater than one-half the sampling frequencyof the analog-to-digital converter 638, as well as frequencies withinone or more adjacent Nyquist zones. The analog-to-digital converter 638can convert the analog downlink reference signal to a digital downlinkreference signal.

The configurable digital filter 640 can modify the downlink referencesignal to generate the downlink mitigation signal as described abovewith respect to FIG. 7. The downlink mitigation signal can removeundesirable signals generated in the downlink communication path 104from the uplink signal. The digital summer 642 can sum the downlinkmitigation signal with the uplink signal. An output (On)) of digitalsummer 642 can be the uplink signal after mitigating undesirable signalcomponents.

A microprocessor executing the adaptation algorithm 644 can iterativelyadjust a frequency response w₁[n] of the configurable digital filter 640and the attenuation provided by attenuator 612 in response to e₁(n) andthe downlink reference signal. The adaptation algorithm 644 can receiveas inputs e₁(n) and the downlink reference signal. Iteratively adjustingthe frequency response of the configurable digital filter 640 can allowthe configurable digital filter 640 to dynamically generate a downlinkmitigation signal in response to the transmission of a downlink signal.Iteratively adjusting the attenuation provided by attenuator 612 canallow attenuator 612 to equalize the signal power of the downlinkreference signal and the undesirable signals recovered by the receiveantenna 107.

FIG. 9 depicts the above-described system with additional circuitry tomitigate from the downlink reference signal one or more signalcomponents at frequencies in the uplink frequency band caused byoverlapping uplink and downlink frequency bands. The transmit antenna106 and the receive antenna 107 may use overlapping frequency bands, forexample, in a DAS 10 that is configured for time division duplexoperation. The transmit antenna 106 and the receive antenna 107 usingoverlapping frequency bands can cause the downlink reference signaltraversing the reference communication path 626 to include signalcomponents at uplink frequencies in addition to undesirable signals.Including signal components at uplink frequencies in the downlinkreference signal can cause the mitigation signal generated using thedownlink reference signal to mitigate or distort uplink signals inaddition to mitigating undesirable signals.

The system depicted in FIG. 9 can remove signal components at uplinksignal frequencies from the downlink reference signal to reduce orprevent the mitigation signal from distorting the uplink signal. In FIG.9, the input to digital-to-analog converter 600 may be used as a secondreference signal. A time delay component 646 can time-delay the secondreference signal. The delay can be equal to the propagation delay of thedownlink reference signal traversing the reference communication path626. The propagation delay can be equal to the delay introduced by thecomponents of both the downlink communication path 104 and the referencecommunication path 626. Delaying the second reference signal can ensurethat the second reference signal is in phase with the downlink referencesignal traversing the reference communication path 626.

The configurable digital filter 648 can modify the second referencesignal to generate a reference mitigation signal. The referencemitigation signal can mitigate signal components at uplink frequenciesin the downlink reference signal traversing the reference communicationpath 626.

The digital summer 650 can sum the reference mitigation signal from theconfigurable digital filter 648 with the downlink reference signaltraversing the reference communication path 626. The digital summer 650can output a modified reference signal (e₂(n)) that does not includeuplink frequency components and that can be the input signal to theconfigurable digital filter 640. The configurable digital filter 640 cangenerate a downlink mitigation signal from modified reference signale₂(n). The downlink mitigation signal can remove undesirable signalcomponents resulting from the downlink communication path 104, asdepicted in FIG. 8, without inadvertently mitigating or distortingsignals on the uplink communication path 108.

A microprocessor using adaptation algorithm 652 can iteratively adjust afrequency response (w₂[n]) of a configurable digital filter 648 inresponse to the modified reference signal e₂(n) and the second referencesignal. The inputs to adaptation algorithm 652 can be the modifiedreference signal e₂(n) and the output signal from time delay component646. Iteratively adjusting frequency response w₂[n] can allowconfigurable digital filter 648 to dynamically generate a referencemitigation signal that correlates substantially with the uplinkfrequency components to be mitigated from the downlink reference signalin the reference communication path 626.

FIG. 10 depicts additional circuitry to remove additional nonlineardistortion from uplink signals following active digital mitigation.Additional nonlinear distortion can result from downlink noisecomponents generated by downlink analog signal processing components inthe downlink communication path 104. The downlink analog signalprocessing components can include the analog filter 602, the mixer 604,the local oscillator 606, the image reject filter 608, and the poweramplifier 610.

Both the uplink signal and the downlink reference signal can include thedownlink noise components at the inputs to the frequency conversioncircuitry in the uplink communication path 108 and the referencecommunication path 626. Frequency conversion circuitry can include theanalog filters 614, 628, the low noise amplifiers 616, 630, the mixers618, 634, the local oscillator 620, the anti-aliasing filters 622, 636,and the analog-to-digital converters 624, 638. Frequency conversioncircuitry in the respective signal paths can create additional nonlineardistortion signals in the uplink communication path 108 and thereference communication path 626 by processing downlink noise componentsin each signal path.

The randomized (i.e., non-periodic) nature of the downlink noisecomponents can cause randomized additional nonlinear distortion signals.Phase-shifting the additional nonlinear distortion signal traversing thereference communication path 626 may not create a mitigation signal thatcan mitigate the additional nonlinear distortion signal traversing theuplink communication path 108. Instead, digital summer 642 may sum theadditional nonlinear distortion signals traversing the uplinkcommunication path 108 and the reference communication path 626. Theoutput of digital summer 642 may be an uplink signal that includes thesummed additional nonlinear distortion signals.

To remove the summed additional nonlinear distortion signals from theuplink signal, configurable digital filter 656 can generate a nonlineardistortion mitigation signal to mitigate additional nonlinear distortionin the uplink communication path 108. The digital summer 642 and theconfigurable digital filter 640 can mitigate other undesirable signalcomponents as depicted in FIG. 8.

FIG. 10 depicts components for generating the nonlinear distortionmitigation signal according to one aspect. A second reference signal canbe time-delayed in the same or similar manner as in FIG. 9. A non-lineartransformation function 654 can generate a distorted reference signalfrom the output of time delay component 646. The distortion fromnon-linear transformation function 654 is proportional to the additionalnonlinear distortion from the downlink analog signal processingcomponents and the frequency conversion circuitry in the uplinkcommunication path 108 and the reference communication path 626.

The configurable digital filter 656 can generate a nonlinear distortionmitigation signal from the distorted reference signal. The nonlineardistortion mitigation signal can mitigate the summed additionalnonlinear distortion signals from the output of digital summer 642traversing the uplink communication path 108.

The digital summer 658 can sum the nonlinear distortion mitigationsignal with the uplink signal. The output of digital summer 658 may be amodified uplink signal (e₃(n)).

A microprocessor having a computer readable medium on which anadaptation algorithm 660 is stored can iteratively adjust frequencyresponse w₃[n] of a configurable digital filter 656 in response to e₃(n)and the second reference signal. The inputs to the adaptation algorithm660 can be modified uplink signal e₃(n) and the output of the non-lineartransformation function 654. Iteratively adjusting the frequencyresponse w₃[n] can allow the configurable digital filter 656 to generatedynamically a mitigation signal that correlates substantially with thesummed additional nonlinear distortion signals traversing the uplinkcommunication path 108.

FIG. 11 depicts additional circuitry for separately mitigating theadditional nonlinear distortion signals traversing the uplinkcommunication path 108 and the reference communication path 626. Theconfigurable digital filter 656 and the digital summer 658 can removethe additional nonlinear distortion signal traversing the referencecommunication path 626. The configurable digital filter 648 and thedigital summer 650 can remove the additional nonlinear distortion signaltraversing the uplink communication path 108.

The configurable digital filter 662 can modify the time-delayedreference signal from a time delay component 646. The configurabledigital filter 662 can attenuate the time-delayed reference signal suchthat the power of the time-delayed reference signal is equal to thepower of the additional nonlinear distortion signal traversing theuplink communication path 108. The output signal of the configurabledigital filter 662 can be the input to non-linear transformationfunction 664. The output signal of the non-linear transformationfunction 664 can be the input to the configurable digital filter 662.

The configurable digital filter 648 can generate a distortion mitigationsignal proportional to the additional nonlinear distortion signaltraversing the uplink communication path 108. The distortion mitigationsignal can mitigate the additional nonlinear distortion signaltraversing the uplink communication path 108. The digital summer 650 cansum the distortion mitigation signal with the uplink signal to mitigatethe additional nonlinear distortion signal traversing the uplinkcommunication path 108. The frequency response of configurable digitalfilter 648 can be optimized as depicted in FIG. 10.

The configurable digital filter 656 and the digital summer 658 canmitigate the additional nonlinear distortion signal traversing thereference communication path 626. The configurable digital filter 656can generate a distortion mitigation signal proportional to theadditional nonlinear distortion signal traversing the referencecommunication path 626. The distortion mitigation signal can mitigatethe additional nonlinear distortion signal traversing the referencecommunication path 626. The digital summer 658 can sum the distortionmitigation signal with the downlink reference signal to mitigate theadditional nonlinear distortion signal traversing the referencecommunication path 626. The output of digital summer 658 can be amodified reference signal after mitigating the additional nonlineardistortion signal traversing the reference communication path 626. Thefrequency response of the configurable digital filter 656 can beoptimized as depicted in FIG. 10.

The configurable digital filter 640 can generate a downlink mitigationsignal from the modified reference signal. The digital summer 642 cansum the downlink mitigation signal with the uplink signal from digitalsummer 650. The output of the digital summer 642 can be the uplinksignal after mitigating both the undesirable downlink signal componentsand the additional nonlinear distortion signals traversing the uplinkcommunication path 108 and the reference communication path 626.

Uplink Gain Adjust

FIG. 12 depicts a method 700 for configuring an uplink gain adjustdevice according to one aspect. The process of FIG. 12 is described withreference to FIG. 3, but other implementations are possible. The uplinkgain adjust device 278 can adjust the gain of the uplink signal inresponse to noise generated by transmit antenna 106. Adjusting the gainof the uplink signal can prevent noise on the uplink communication path108 from distorting the uplink signal.

In block 702, a threshold is calculated using a maximum noise floor inthe uplink communication path 108 and the power of the noise signal inthe uplink communication path 108. A noise floor may be the power of thenoise signal in the uplink communication path 108 created by all sourcesof noise. The sources of noise can include noise from the devices in theuplink communication path 108 and any downlink noise component from thedownlink communication path 104. The uplink signal can be distorted bythe noise floor exceeding the minimum power of an uplink signal. Amaximum noise floor can be specified as a noise floor at some valuebelow the minimum uplink signal amplitude. The threshold may be thepower of the downlink noise that can cause the noise floor to exceed themaximum noise floor.

The noise floor can be determined in part by the power of the uplinknoise. To measure the uplink noise signal power, a test uplink signalcan be transmitted from a mobile device and recovered by the receiveantenna 107. In some aspects, a noise figure meter can be used tomeasure the power of the uplink noise signal directly. In other aspects,a spectrum analyzer with appropriate hardware and software can be usedto determine the spectral composition of the test uplink signal. Thespectrum analyzer can be communicatively coupled to a microprocessor orsimilar device. The microprocessor can execute a software program toanalyze the spectral composition of the test uplink signal and determinethe power of the uplink noise signal.

The threshold can be calculated as the difference between the maximumnoise floor and the power of the uplink noise signal. A microprocessoror similar device can execute a software program to calculate thethreshold. The inputs to the software program can include the power ofthe uplink noise signal and the maximum noise floor. In some aspects,the microprocessor calculating the threshold can be the same as, orcommunicatively coupled to, a microprocessor that can determine thepower of the uplink noise signal.

In block 704, the downlink noise present on the uplink communicationpath is determined. In some aspects, the downlink noise can bedetermined by transmitting a test downlink signal on the downlinkcommunication path 104. The test downlink signal can cause a downlinknoise component on the uplink communication path 108. A computing devicefor determining the downlink noise power can be coupled to the uplinkcommunication path 108 at the output of mixer 272. In other aspects, thedownlink noise component can be dynamically determined during operationof DAS 10. For example, a computing device for determining the downlinknoise component power as downlink signals are transmitted can be coupledto the downlink communication path 104 at transmit antenna 106.

In some aspects, the downlink noise can be measured directly with anoise figure meter. In other aspects, the downlink noise can bedetermined using a spectrum analyzer with appropriate hardware andsoftware.

In block 706, the downlink noise is compared to the threshold todetermine whether the downlink noise exceeds the threshold. Amicroprocessor or similar device can execute a software program tocompare the threshold and the downlink noise. The software program canreceive or access the threshold from memory and can receive or determinethe downlink noise. In some aspects, the microprocessor can becommunicatively coupled to the computing device for determining thethreshold and the computing device for determining the downlink noise.

If the downlink noise exceeds the threshold, the uplink gain adjustdevice 278 can adjust the uplink gain adjust device in block 708 toamplify the uplink signals sufficiently to increase the minimum uplinksignal power above the noise floor. If the downlink noise component doesnot exceed the threshold, no gain adjust is applied as in block 710. Inaspects including a dynamic measurement of the downlink noise in block704, blocks 704 through 710 can be executed iteratively during operationof DAS 10.

Block 708 can be implemented by uplink gain adjust device 278. In someaspects, the uplink gain adjust device 278 is a variable gain amplifier.A variable gain amplifier can vary a gain in response to a controlvoltage from a voltage source. In some aspects, the control voltage canbe selected by an external controller. An example of an externalcontroller is a computing device, such as a laptop or a server, that iscommunicatively coupled to uplink gain adjust device 278. In otheraspects, the control voltage can be selected by a microprocessordisposed in a master unit.

In other aspects, the control voltage is selected by a single physicalstep, such as in response to turning a dial. In aspects where thecontrol voltage is selected by a single physical step, themicroprocessor of block 706 may display a suggested or needed gainadjust to a technician responsible for configuring uplink gain adjustdevice 278.

In some aspects, one or more communicatively coupled microprocessors mayexecute software programs corresponding to blocks 702 through 704. Inother aspects, a single microprocessor communicatively coupled toappropriate measurement instrumentation may execute the softwareprograms corresponding to blocks 702 through 704.

The foregoing description of the aspects, including illustrated aspects,of the invention has been presented only for the purpose of illustrationand description and is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. Numerous modifications,adaptations, and uses thereof will be apparent to those skilled in theart without departing from the scope of this invention.

What is claimed is:
 1. A method comprising: receiving a downlinkreference signal from a downlink path; generating, by a non-duplexerisolator sub-system, a mitigation signal from the downlink referencesignal by mitigating uplink frequency components in the downlinkreference signal; and mitigating, by the non-duplexer isolatorsub-system, downlink frequency components in an uplink signal traversingan uplink path by combining the mitigation signal with the uplinksignal.
 2. The method of claim 1, wherein mitigating the uplinkfrequency components comprises generating an additional mitigationsignal with the uplink frequency components and combining the additionalmitigation signal with the downlink reference signal.
 3. The method ofclaim 2, wherein generating the additional mitigation signal comprises:receiving an additional downlink reference signal from the downlinkpath; and mitigating downlink frequency components in the additionaldownlink reference signal to obtain the additional mitigation signal. 4.The method of claim 3, wherein the additional downlink reference signalis a digital downlink signal received from a point in the downlink pathprior to a digital-to-analog converter and wherein mitigating thedownlink frequency components comprises digitally filtering theadditional downlink reference signal to attenuate the downlink frequencycomponents.
 5. The method of claim 1, further comprising: generating anonlinear distortion mitigation signal; and mitigating nonlineardistortion in the uplink signal by combining the nonlinear distortionmitigation signal with the uplink signal.
 6. The method of claim 5,further comprising: generating an additional nonlinear distortionmitigation signal; and mitigating nonlinear distortion in the downlinkreference signal prior to generating the mitigation signal from thedownlink reference signal, wherein the nonlinear distortion in thedownlink reference signal is mitigated by combining the additionalnonlinear distortion mitigation signal with the downlink referencesignal.
 7. A non-duplexer isolator sub-system comprising: a mitigationsub-system configured for: receiving a downlink reference signal from adownlink path, generating a mitigation signal by mitigating uplinkfrequency components in the downlink reference signal, and mitigatingdownlink frequency components in an uplink signal traversing an uplinkpath by combining the mitigation signal with the uplink signal.
 8. Thenon-duplexer isolator sub-system of claim 7, wherein the activemitigation sub-system comprises: a first digital summer communicativelycoupled to the downlink path and configured for mitigating the uplinkfrequency components in the downlink reference signal; and a seconddigital summer included in the uplink path and communicatively coupledto the first digital summer, wherein the second digital summer isconfigured for combining the mitigation signal with the uplink signal.9. The non-duplexer isolator sub-system of claim 8, wherein the activemitigation sub-system further comprises a digital filter coupled betweenthe downlink path and the first digital summer, wherein the digitalfilter is configured for generating an additional mitigation signalhaving the uplink frequency components and the first digital summer isconfigured for combining the additional mitigation signal with thedownlink reference signal.
 10. The non-duplexer isolator sub-system ofclaim 9, wherein the digital filter is configured for generating theadditional mitigation signal by mitigating downlink frequency componentsin a digital downlink reference signal received from the downlink path.11. The non-duplexer isolator sub-system of claim 7, wherein the activemitigation sub-system is further configured for: generating a nonlineardistortion mitigation signal; and mitigating nonlinear distortion in theuplink signal by combining the nonlinear distortion mitigation signalwith the uplink signal.
 12. The non-duplexer isolator sub-system ofclaim 11, wherein the active mitigation sub-system is further configuredfor: generating an additional nonlinear distortion mitigation signal;and mitigating nonlinear distortion in the downlink reference signalprior to generating the mitigation signal from the downlink referencesignal, wherein the nonlinear distortion in the downlink referencesignal is mitigated by combining the additional nonlinear distortionmitigation signal with the downlink reference signal.
 13. Thenon-duplexer isolator sub-system of claim 12, wherein the activemitigation sub-system comprises: a plurality of digital filtersconfigured for generating the mitigation signal, the nonlineardistortion mitigation signal, and the additional nonlinear distortionmitigation signal; a plurality of digital summers configured forcombining the mitigation signal with the uplink signal, combining theadditional nonlinear distortion mitigation signal with the downlinkreference signal, and combining the nonlinear distortion mitigationsignal with the uplink signal.
 14. The non-duplexer isolator sub-systemof claim 13, further comprising a reference path between a point on thedownlink path and a digital summer configured for combining themitigation signal with the uplink signal, wherein the reference pathcomprises down-conversion circuitry and an analog-to-digital converterconfigured for generating the downlink reference signal from an analogdownlink signal sampled from the downlink path.
 15. A non-duplexerisolator sub-system comprising: a mitigation sub-system configured for:generating a mitigation signal from a downlink reference signal receivedfrom a downlink path, generating a nonlinear distortion mitigationsignal from a digital downlink reference signal received from thedownlink path, and mitigating downlink frequency components andnonlinear distortion in an uplink signal traversing an uplink path bycombining the nonlinear distortion mitigation signal with the uplinksignal.
 16. The non-duplexer isolator sub-system of claim 15, whereinthe active mitigation sub-system is further configured for: generatingan additional nonlinear distortion mitigation signal; and mitigatingnonlinear distortion in the downlink reference signal prior togenerating the mitigation signal by combining the additional nonlineardistortion mitigation signal with the downlink reference signal.
 17. Thenon-duplexer isolator sub-system of claim 15, wherein the activemitigation sub-system is configured for generating the mitigation signalby mitigating uplink frequency components in the downlink referencesignal.
 18. The non-duplexer isolator sub-system of claim 15, whereinthe active mitigation sub-system comprises: a first digital filtercommunicatively coupled to the downlink path and configured forinverting the downlink reference signal to generate the mitigationsignal; a first digital summer included in the uplink path andconfigured for combining the mitigation signal with the uplink signal; asecond digital filter communicatively coupled to the downlink path andconfigured for generating the nonlinear distortion mitigation signal; asecond digital summer included in the uplink path and configured forcombining the nonlinear distortion mitigation signal with the uplinksignal.
 19. The non-duplexer isolator sub-system of claim 18, whereinthe active mitigation sub-system further comprises: a third digitalfilter configured for generating an additional nonlinear distortionmitigation signal; and a third digital summer included in a signal pathfrom the downlink path to the first digital filter and configured forcombining the additional nonlinear distortion mitigation signal with thedownlink reference signal.
 20. The non-duplexer isolator sub-system ofclaim 18, wherein the active mitigation sub-system further comprises areference path between a point on the downlink path and the firstdigital summer, wherein the reference path comprises down-conversioncircuitry and an analog-to-digital converter configured for generatingthe downlink reference signal from an analog downlink signal sampledfrom the downlink path.